Reverse Nodes in K-Group

def reverseKGroup(self, head: Optional[ListNode], k: int) -> Optional[ListNode]: dummy = ListNode(0, head) def get_kth_node(node, n): if node is None: return None, None cur = node while n: n -= 1 node = node.next if node is None: # Group where length is less than k return None, None return node, node.next def reverse(node): prev, curr = None, node while curr: nxt = curr.next curr.next = prev prev = curr curr = nxt return prev prev_tail, prev_prev_tail = None, None first = True while True: kth, next_head = get_kth_node(head, k - 1) if kth is None and next_head is None: prev_tail.next = head break kth.next = None prev_prev_tail = prev_tail prev_tail = head new_reversed_head = reverse(head) if first: dummy.next = new_reversed_head first = False else: prev_prev_tail.next = new_reversed_head head = next_head return dummy.next